This invention relates to an optical component the characterizing feature of which is specified in claim 1, and to a method per claim 9 for fabricating such an optical component.
Optical components are widely employed for instance in the realm of telecommunications. These components may be in the form of solid modules performing an optical function for which they feature at least one optically functional surface. However, these components may also contain moving parts so that they must additionally satisfy certain mechanical requirements. A typical example where mechanically moving elements must be accommodated is the optomechanical switch which is frequently employed in telecommunications systems. These components must usually meet rigid requirements in terms of functional precision and, consequently, of the precision with which they are manufactured. In many cases, particularly demanding requirements must be met with regard to the attainability and maintainability of the desired level of their reflective properties and to their angular tolerances.
As employed in prior art, components of this type can be produced as one-piece light-metal elements whenever the optical surface is to be reflective. To that effect, a plane reflective surface can be produced in the appropriate region of the element and may be given a mirror polish. The reflective surface must be particularly smooth, i.e. level with a minimum of surface roughness so as to prevent light scattering, given that in general the mirrors produced are quite small, with surfaces typically on the order of 3xc3x9710^2 or less. Fabricating that type of mirror involves relatively complex metal-working processes such as diamond-machining in order to obtain the necessary surface quality and surface precision. This entails a relatively high cost of production and perhaps a correspondingly high reject rate.
To avoid this disadvantage, the German utility patent GB 20010594.9 introduces an optomechanical switch in which the component consists of a base unit without any optically functional surface but provided with a glass substrate which does have an optically functional surface. It is thus possible to produce high-quality glass surfaces at low cost employing conventional polishing techniques, obviating the need for any complex metalworking processes for producing the reflective components. Reference is made to established, sophisticated methods for coating this type of glass element with a highly reflective, optically excellent mirror surface. In this fashion, as the document explains, it is possible to polish, clean and coat glass substrates, and according to an enhanced version of that invention, the process also permits the reflective coating of large glass substrates. In thin-film technology, for example, the method of preference is usually to coat large substrates which, after the coating, are cut to size and separated into numerous small components. The advantage of this approach lies in the fact that loading and unloading large substrates on the coating equipment requires fewer operating steps, thus reducing the time needed for loading the coating equipment. Moreover, every substrate must be placed on a support, where the necessary tooling is more easily implemented for large substrates. Each such support is of a particular geometric size and occupies in the coating machine an area that cannot be utilized for the coating of substrates. Where for small substrates a great many supports are needed, they usually occupy a large combined area. It follows that when coating large substrates, the effectively coated substrate area is at times larger by a multiple factor.
One advantage of the approach described in the utility patent is the separation of the mirror-coating process from the fabrication of the base unit. Producing the base unit is thus made easier, more efficient and more cost-effective. This separation does have a drawback in that the substrates, once coated, must then be cut to size, separated and mounted on the base unit. The term mounting in this case refers to the assembly of two or more parts into one component which is appropriately called an assembly. The mounting process typically involves numerous handling operations, such handling including the grasping, conveying, relocating and in general the manipulation of parts. In some cases it is necessary to apply layered systems which offer only marginal resistance to mechanical or chemical effects. This is particularly disadvantageous when the assembly process does not make it possible, or at substantial expense only, to avoid such effects, or whenever the assembly process leads to the need for another cleaning. If the coating is damaged in the process, the optical component will of course be of a lower quality and in case of doubt it may have to be scrapped.
It is the objective of the invention here presented to eliminate the drawbacks inherent in prior art. As a particular objective, the optical component is to be so constructed that any handling and assembly problems can be avoided or minimized without compromising the required high level of optical precision of the component, while the production method employed is to be highly cost-effective.
According to the invention, the objective is achieved by the approach taken per claims 1 and 9. The subclaims cover desirable enhancements.
In the approach according to this invention, the coating of the substrates supporting the optically functional surface is moved as close as possible to the end of the process chain, which is accomplished by coating not only the substrates but the assembled component as a whole. Accordingly, the process of fabricating the optical component can be summarized to include the following steps:
a) Manufacturing the base unit;
b) Producing a substrate with an optical surface;
c) Attaching the substrate to the base unit, preferably by cementing it on, to thus make up the component;
d) Coating the component, including the optical surface of the substrate, by a vacuum coating process.
The result is an optical component consisting of a base unit supporting a substrate of which at least one region features an optically functional surface coated with a reflective layer in such fashion that the said coating extends at least in part beyond the substrate and onto the base unit. The optically functional surfaces concerned include in particular those surfaces which, depending on their intended optical function, reflect, transmit, absorb, refract or diffract the incident light. Hence, the optically functional surface may be a mirror, a color filter, a polarizing beam splitter, a lens or in general any refractive or diffractive element. In many cases, as yet uncoated substrates are less susceptible to damage by mechanical or chemical effects than are coated substrates. It follows that an uncoated substrate can be accurately mounted by means of a correspondingly precise assembly device. The process allows for the optically functional surface of the substrate and a fiducial reference point on the base unit to be mutually aligned in predefined fashion, with emphasis on precise orientation. In other words, the reflective substrate region on the optical component is positioned in predefined fashion relative to a reference point on the base unit. This reference point is preferably constituted of two plane reference surfaces. The substrate is preferably cemented onto the base unit. The cement layer bonding the substrate with the base unit fixes the orientation and can in fact serve to correct for variations in the space between the substrate and the base unit. Therefore, the surface regions on the substrate and on the base unit which are to be bonded together do not have to be perfectly precise for the purpose of orientation, which in turn simplifies the production of both the substrate and the base unit.